The Baudelaires stay with her and Mr. Poe prior to living with Count Olaf. She buys a lot of itchy and ugly clothing for them.
Mr. Poe also adds "Call my wife!" to the list of random cries for help he utters in The Reptile Room when he thought that Sunny had been poisoned by the Incredibly Deadly Viper.
At one point Mr Poe says that he will tell his wife that dark is in, indicating that she is quite a fashionable woman, or at least tries to be. Mr. Poe is even willing to pay $409 for an ocean decoration of a red herring, likely for her.
In the TV series, Polly Poe's role as Mr. Poe's wife has been removed, with Eleanora Poe (portrayed by Cleo King) now being his wife instead of his sister.
There is a character named Polly Partial in All the Wrong Questions. It is possible they are the same character, that Polly Partial married Mr. Poe and took his last name. However, since Polly Partial is depicted as an older woman when Lemony Snicket was 12, it is unlikely that she could have had children a decade later with Mr. Poe.